Most North Jerseyans only notice the Hackensack River when they're stuck in traffic on one of the many bridges that span it. And what they see often is the river at low tide, when it looks like a junk-strewn mud flat.

But appearances are deceptive. After centuries of development, dumping and damming, the 50-mile-long river is turning the corner.

The Hackensack's southern half, used as an open sewer for decades, is making a spirited comeback. The relatively pristine northern half, which provides the drinking water to 750,000 New Jerseyans, is benefiting from new safeguards against development and pollution.

"If you look at the big picture of what is happening with the river, a lot of things are improving," says Narinder Ahuja, director of the state Department of Environmental Protection's Division of Water Quality.

"We have come a long way," he says, then adds: "But we are not there yet."

"You can see the birds are coming back, the fish are coming back," he says. "And the water is getting cleaner, though heaven knows it'll take years to get rid of the really bad stuff. But I've canoed and kayaked the river, tipped my boat over, and lived to tell the tale."

A few signs that the tide has turned:

• A study released this spring found that the river bottom had significantly fewer harmful metals from industrial dumping than it did 20 years ago. Although the mercury levels still exceed federal limits, chromium, cadmium, copper and lead contamination decreased by an average of 75 percent, according to the study by the New Jersey Meadowlands Commission, which regulates 14 miles of the river south of the Route 46 bridge.

• More kinds of fish are living in the lower Hackensack. A decade ago, about the only fish that could survive were mummichog, a pollution-resistant bait fish. Now researchers say perch, striped bass and other game fish are making the river their home again.

• This summer, ospreys successfully nested on the river for the first time in 50 years. Cliff swallows, bald eagles and peregrine falcons are also living on the Hackensack again now that the fish and other foods are becoming more plentiful.

• As the river turns from a dump into a recreation area, more visitors are discovering just how breathtaking the Hackensack can be. Municipalities are building walking paths along the river. In the past year, the Hackensack Riverkeeper, a non-profit group that has championed the river's renaissance, has brought 5,000 people to the river on pontoon-boat eco-cruises, kayaks and canoes, and on walking tours. The New Jersey Meadowlands Commission has taken another 2,200 on tours of the river and marshes.

"People just now are starting to rediscover these places that people have kind of turned their backs on over the past century," says Jerry Willis of the National Park Service. "They looked at these places as places to be avoided, and now people are rediscovering them as places that can be enjoyed. Given the Hackensack River's location, it is a huge recreational resource in the rough."

But the river has a long way to go.

While fish and crabs have returned below the Oradell Dam, they're contaminated – white perch, for instance, have PCB levels 10 times greater than national guidelines for safe eating. Even the scenic reservoirs have problems: United Water recently warned customers the drinking water contains high levels of sodium, runoff from the salt spread on roads during winter storms.

And although the river looks cleaner, some sections remain mired in litter. United Water spends $500,000 a year on booms and cleanup crews to keep trash out of its drinking water supply. The company estimates it fishes out tens of thousands of cigarette butts a year. The Riverkeeper has hauled out an estimated 120 Dumpsters' worth of debris in the past decade, but they and other volunteers can't keep up with the trash.

So much illegal dumping still occurs in the Meadowlands that police officers are being hired to patrol the marshes.

"As I drive around the Meadowlands, I'll see a refrigerator door, an AC unit, some old ceramic tile, and I just know somebody came out with their pickup truck and dumped it there," says Gabrielle Bennett-Meany, a naturalist for the Meadowlands Commission.

Toxic twists and turns

The word Hackensack comes from the Leni-Lenape word Atchensehaky, which means "river of many bends."

It begins as a brook in New York State and feeds three major reservoirs as it winds through Bergen County before emptying into Newark Bay.

The waterway's past has had as many twists as the river itself.

The river provided an abundance of striped bass, herring and shad for Native Americans and the European settlers who sailed up the Hackensack in the early 1600s. It served as the main road in the area, and a thriving commercial boat trade developed.

As the population grew, development began to take its toll. Marshes were diked to create farmlands. Cornelius Mattyse, the first owner of the property that is home to the historic Steuben House in River Edge, was a professional land clearer.

"This all had a dramatic effect on the runoff and the discharges into the river," says regional historian Kevin Wright. "By the 1750s, it was already noted that water levels were changing dramatically. The water was being used for agriculture, and removing the forests and marshes changed the land's ability to retain water."

As North Jersey evolved from farms to suburbs and autos became the preferred means of transportation, residents began turning their backs on the river.

The Hackensack became a dumping ground. Towns ran their sewage pipes to the water's edge.

"What really killed the Hackensack River was suburban sewage," Wright says. "Until the 1920s, this was a white-sand bottom river. Once you layer the bottom with muck, it kills all the bottom feeders, and when you kill them you kill everything on up the food chain."

In the 1920s, the Hackensack Water Co. (now United Water) built the Oradell Dam, turning the Hackensack into two rivers – fresh water to the north, a brackish estuary of Newark Bay to the south. Although the reservoir system provided the drinking water necessary for the region, that water came at a price.

The building of the Oradell Dam "is a poster child for why strong environmental regulations were needed in the first place," says Bill Sheehan, head of the Hackensack Riverkeeper. "The flow of the river was interrupted with no consideration of the consequences."

With the river no longer running steadily, salt water from Newark Bay pushed farther upstream toward the Oradell – killing off freshwater fish and plants and causing major sedimentation problems.

The Meadowlands became home to more than 30 garbage dumps, destroying thousands of precious acres.

Industry also took a toll on the river. In one instance, part of a paper factory in Ridgefield Park extended over the river, and the floor drains emptied directly into the Hackensack. In Wood-Ridge, so much waste was dumped into a tributary of the Hackensack that Berry's Creek earned the terrible distinction of having the highest freshwater concentration of mercury contamination recorded anywhere in the world.

Scientific Chemical in Carlstadt, Diamond Shamrock and Standard Chlorine in Kearny and others left a legacy of pollution that remains to this day. Dioxin, chromium, asbestos, benzene and PCBs leached into the Hackensack River for decades.

Most of these sites have yet to be cleaned up because of litigation and backlogs – and because they are so contaminated that nobody can agree on how to rid the pollution from the river.

"The sites are incredibly frustrating," says Robert Ceberio, executive director of the Meadowlands Commission. "Some haven't seen significant progress in nearly 30 years. The legal challenges have become so strong and so deep that cleanup efforts are nearly crippled. As an agency, all we can do is test the wetlands and waterways around these sites to determine the extent of environmental impacts of the pollution."

Cleanup duty

State officials knew as far back as 1941 that the Hackensack was in trouble. The State Planning Board noted that the Hackensack and other rivers had been "grossly abused." It proposed a park in the Meadowlands, calling them "a priceless public asset."

But the proposal got tied up in red tape and inertia. It took the federal Clean Water Act of 1972 to stop government and industry from unchecked dumping.

Given a chance, the river is slowly cleansing itself. With less pollution to absorb, the Hackensack's marshes are better able to act as filters for sewage and other organic pollutants.

Some of the cleanup work is imaginative: Thousands of oysters are being planted by the Meadowlands Commission in the mud along the lower Hackensack to fight pollution. An adult oyster can filter 50 to 60 gallons of water a day.

The fact that oysters are living in the river is good news in itself. Until recently, the river was too polluted for them to survive.

Other efforts are costing hundreds of millions of dollars.

Bergen County is spending $70 million to treat an estimated 39,000 gallons a day of leachate that had been seeping from the old landfill in Overpeck County Park and making its way into the river.

PSE&G's Ridgefield power plant, meanwhile, received an extreme makeover. The plant used to suck up and then spit out river water to use as a coolant. It now uses treated wastewater from the nearby Bergen County Utilities Authority plant to cool the generators.

Before the switch, that stretch of river was "a dead zone for fish," says Hugh Carola of the Hackensack Riverkeeper. "The water PSE&G discharged was way too warm, with way too little oxygen for fish to survive."

PSE&G is spending $700 million to install state-of-the-art pollution control equipment at its Hudson Generating Plant on the Hackensack in Jersey City. The plant still uses coal to power one of its generators – which causes pollution that can settle in waterways. The project includes new water-intake screens to keep fish from getting killed.

The BCUA, which treats the sewage of 46 municipalities, upgraded its Little Ferry sewage treatment plant in 1999. The area can still smell when you pass by in a boat, but the plant no longer uses heavy doses of chlorine to disinfect the wastewater before discharging it into the river. Now it uses calcium hypochlorite, a chemical that breaks down a lot faster.

The BCUA has also upgraded two sewer overflows at New Bridge and Overpeck Creek so they no longer dump raw sewage into the Hackensack during heavy rains. Next to be upgraded in 2010: the Forest Avenue overflow in Englewood, which sometimes sends untreated sewage into the Overpeck, which feeds into the Hackensack.

Still, sewage remains the river's nemesis. Hackensack, Ridgefield Park, North Bergen and Jersey City together have 27 overflow sewer system points on or by the river. The storm water and raw sewage from the combined sewer systems flow through the same pipes to the treatment plants -- and when heavy rains hit, the sewers back up and the plants are forced to release some diluted sewage into the river.

Ridgefield Mayor George Fosdick says the impact of his town's combined sewers has been exaggerated but adds: "We're doing all we can. We love the river."

North Bergen plans to begin sending its sewage to the Passaic Valley Sewerage Commission plant in Newark. But it will travel via Jersey City's combined sewer system -- which has the same overflow problems.

The DEP's Narinder Ahuja says the agency is working with the municipalities on the combined sewer problem but would not commit to a timetable. "The tangible results you're not going to see the next day," he says. "It takes time. But it will show."

External threats

In short, the river's renaissance has a long way to go.

Even the reservoirs – which provide 112 million gallons of water a day, 172 million on peak summer days, to residents in Bergen and Hudson counties -- are in a constant struggle against the damage caused by man.

Water from these reservoirs is getting saltier – to the point where United Water was required this summer to warn customers on sodium-restricted diets.

The water company blames the problem on decades of salt spread on thousands of roads in the watershed. They're hoping to convince towns near the reservoirs to switch to healthier – though far costlier – methods of clearing the roads of snow and ice.

To improve the quality of the drinking-water, United Water is spending $110 million to add a pre-purification process to remove more solids, most notably algae, at its Haworth water-treatment facility and to computerize the entire reservoir system. The upgrades come at a price: The company wants a 28 percent rate increase.

To protect the reservoirs, New Jersey implemented rules three years ago to prevent development within 300 feet of tributaries that lead into drinking-water supplies. Known as Category One regulations, these buffer zones help prevent pollution from getting into the drinking supply.

But development continues to encroach: Homeowners have surreptitiously cut down these buffer zones.

In River Vale, meanwhile, three parcels of former water company land that aren't covered by these regulations are earmarked for development. Developers want to build 78 town houses and 12 single-family homes on land not far from the Lake Tappan Reservoir. Environmentalists want the acres preserved as open space.

"Every last inch of open space is critical to preserve at this point because we are a heavily developed watershed," says Lori Charkey of Bergen SWAN, a citizens group dedicated to fighting what they consider inappropriate development in the watershed.

The developers have insisted that appropriate measures have been taken to make sure the developments don't have a negative impact.

Then there's all that litter in many parts of the river. The state has passed a rule requiring storm drains to have grates to prevent debris from washing into the river. But it will take years to implement because those grates don't have to be added until a street is repaved.

"The biggest impediment to our reservoirs is the non-point pollution," says United Water spokesman Rich Henning. "It's the trash mindlessly thrown out the car window that washes into the storm sewer, then washes into our waterways."

Reaching out to the public

How long the river will take to recover from centuries of abuse is hard to gauge. The DEP says the sewage problems will take several years, and the storm-drain litter will take even longer. Dealing with the toxic materials buried in the river or within its reach could take decades or more.

Then there is the unforeseen. "What worries us, being in a very urban environment, are human-made catastrophes -- oil spills, fecal coliform from oversaturated water treatment plants, contamination from spills from factories," says Francisco Artigas, director of the Meadowlands Environmental Research Institute.

Making the Hackensack pristine again may be next to impossible, experts say, but the river has reached a point where people can appreciate and enjoy it.

To help convince people of the river's value, Hackensack Riverkeeper is teaming with the National Park Service's Rivers and Trails Program to create a 21-mile-long paddling route from Oradell to Jersey City. It would have a dozen launch sites for kayakers and canoeists, plus road signs and maps to point them in the right direction.

More than 60 years after the state recommended a park in the Meadowlands, plans are afoot to turn 8,400 acres into a natural area.

"In order to protect the river, you need to have people who know about the river and care about the river," says Jordan Wouk, who helped create Teaneck's 3½-mile greenway. The pedestrian walkway, which includes plaques explaining the river's rich history, also provides a buffer between the municipality's developed area and the water's edge.

But the public's rediscovery of the Hackensack and its marshes comes with a fear of unintended consequences.

"Two Jet Skiers today might not make a difference, but if the number of Jet Skiers multiplies over time, how will they know where the endangered species are nesting?" asks Gabrielle Bennett-Meany, the NJMC naturalist. "How close will they get to where nature persists?"